A truism is a claim that is so obvious or self-evident as to be hardly worth mentioning, except as a reminder or as a rhetorical or literary device, and is the opposite of falsism.In philosophy, a sentence which asserts incomplete truth conditions for a proposition may be regarded as a truism. An example of such a sentence would be "Under appropriate conditions, the sun rises." Without contextual support – a statement of what those appropriate conditions are – the sentence is true but incontestable. A statement which is true by definition ("All cats are mammals.") would also be considered a truism. This is quite similar to a tautology in which the conclusion of a statement is essentially equivalent to its premise, a statement that is "true by virtue of its logical form alone".The word may also be used with a different sense in rhetoric, to disguise the fact that a proposition is really just an opinion. Similarly, stating an accepted truth about life in general can also be called a truism.